Often it is useful to detect target materials on the basis of certain properties of those target materials, for example, size or mass. Target materials can be labelled and then may be detected by using a probe. Alternatively, target materials may be stained and detected based on the properties of the stain. However, when it is desirable to detect target materials on the basis of the size of the target materials, a filter, particularly, a hydrodynamic filter is useful. A hydrodynamic filter is a system for capturing target materials in a fluid by flowing the fluid through the filter. There is a need for hydrodynamic filters and related compositions or methods for effectively detecting target materials.